The present invitation relates to the removal of an immiscible fluid in a water continuous phase. In particular, the invention relates to the cleanup of hydrocarbons in water that is produced with crude oil before the water is discharged to a disposal area or to an injection well. Attempts to remove oil from the water by providing retention time with large tanks or flumes have not been successful. Tanks or flumes with theoretical retention times large enough to accomplish removal of small oil droplets dispersed in the oil continuous phase are subject to severe short circuiting due to temperature and density difference.
In U.S. Pat. No. 3,893,918 issued July 8, 1975 there are disclosed skim piles or elongated separator conduits that are useful in such operations. In that design there is a plurality of closely spaced baffle plates to induce coalescence of droplets of oil in the water. With each passing of a baffle some of the coalesced oil droplets rise to a quiescent zone on the underside of the previous baffle where they are recovered and transported to the top of the conduit.
The present invention utilizes a plurality of coalescing pipes instead of baffles to create the turbulence between each section of the vertical flume. The retention time of the water while flowing through these pipes is much greater than the retention time of the water while flowing around the edge of a baffle. Since coalescence is known to be a time dependent phenomena, flow through the coalescing pipe is significantly more efficient at increasing the diameter of the oil droplets to be separated from the water and thus fewer stages of separation are required than in the previous patent.
The coalescing pipes also cause abrasion of sand or solid particles with each other and with the pipe walls. This cleans the solids of oil attached to them with each passage through the coalescing pipes. The oil drops which are abraded from the solids become dispersed in the water where they coalesce and are separated out in a treating zone.
The length and diameter of the coalescing pipes can be determined to provide appropriate drop size growth. In the baffle design of the previous patent it is not possible to predict ahead of time the degree of drop size growth that will occur as the water flows round the edge of each baffle. Thus, the present invention is an improvement on the existing patent by providing for better coalescence per stage and thus requiring fewer stages to treat the water. In addition, the amount of abrasion which is experienced by solid particles is increased, making for an improvement in treating oil from the solids contained in the water. Finally, the process follows defined physical and empirical laws which allows the engineer to size the installation with a high degree of comfort that it will function in the required manner.